WO 95/24102 discloses a method for prioritizing calls in a mobile radio system in which a higher transmitting power is used for calls with high prioritization than for calls with lower priority. In the case of the calls with high priority, the transmission power is in each case increased by a constant amount. In EP 0 565 507 A, access bursts are transmitted in a mobile radio system in order to minimize interference at relatively low power. If the message is not detected, it is retransmitted with an in each case increasing power level until it is finally detected.
In radio communication systems, messages (for example voice, picture information or other data) are transmitted via a radio interface with the aid of electromagnetic waves. The radio interface relates to a connection between a base station and subscriber stations, where the subscriber stations can be mobile stations or stationary radio stations. The electromagnetic waves are radiated by carrier frequencies which are within the frequency band provided for the respective system. For future radio communication systems, for example the UMTS (Universal Mobile Telecommunication System) or other third-generation systems, frequencies are provided in the frequency band of approx. 2000 MHz.
A random access channel (RACH) of a radio communication system is characterized by the access to this channel not being coordinated. The mobile stations of a radio cell can use this channel without prior allocation in order to request, for example, a subsequent allocation of radio resources, e.g. when setting up a connection.
Due to the uncoordinated access, however, collisions occur between the transmissions of the individual mobile stations. If the transmissions of a number of mobile stations become superimposed in a receiving base station, the transmissions are no longer detectable and thus the mobile stations do not receive an acknowledgement of the transmission.
After a collision, the mobile stations attempt to retransmit in the random access channel. The more frequently the access has to be repeated, the longer the waiting time and the lower the efficiency of this access method.
DE 198 17 771 discloses admitting access blocks which are orthogonal to one another in time and reducing the probability of a collision by selecting one of a number of different access blocks, i.e. of different transmitting times within the channel.
ETSI SMG2 UMTS L1 Expert Group, Tdoc SMG2 UMTS-L1 455/98, Oct. 14, 1998, discloses another possibility for improving the efficiency of the described method. In this document, it is proposed to provide an incremental increase in power. The mobile station begins with a transmitting power which is reduced with respect to the normal power setting and incrementally increases the transmitting power until reception is acknowledged by the base station.